Move result logging to log file

Hello Camme,

Fantastic library. I wonder if this patch might be considered.

A project requirement (integration with an existing cucumber test framework that was previously running in seleniumRC) highlighted a need to be able custom manage results/errors returned in proxyResponse.

This patch moves result logging code from RequestHandler.js(proxyResponse()) to log.js(log.result) which enables results and errors to be custom managed like so;-

client = webdriverjs.remote();
client.log.result = function(result, data, callback){
   //code here
}

Regards,

Clara